1. Field of the Invention
The present invention relates to an apparatus for driving an extruder that is typically represented by a twin continuous kneader for kneading high-molecular resin materials such as plastics and rubber.
2. Description of the Related Art
One known apparatus for driving a resin molding machine comprises a main motor; a planetary gear mechanism including a torque input portion driven by the main motor and an output portion for outputting a driving force after reducing a rotational speed (rpm) of the main motor; an output distributing gear mechanism for distributing the driving force from the output portion of the planetary gear mechanism to a plurality of rotor drive shafts arranged parallel to each other; coupling means for connecting one ends of the rotor drive shafts to a plurality of rotors on the extruder side; and thrust bearings for supporting the other ends of the rotor drive shafts to bear thrust forces from the rotors (see, for example, Japanese Unexamined Patent Application Publication No. 11-115035).
In such an extruder driving apparatus, the main motor is generally constituted by a motor rotating at a constant speed and having a large capacity for the necessity of driving the rotor drive shafts with a very large torque.
To meet a need of changing the number of poles of the main motor or changing the rotational speed of each rotor drive shaft depending on the specifications of extruders, therefore, a speed change gear mechanism (see gears 19 and 20 in the above-cited publication) is provided which enables one pair of gears to be replaced by another pair having a different gear ratio for adjustment of the rotational speed of each rotor drive shaft. The speed change gear mechanism is conventionally disposed between the main motor and the planetary gear mechanism.
However, when the speed change gear mechanism is disposed between the main motor and the planetary gear mechanism, the rotational speed of the speed change gear mechanism is equal to or greater than that of the main motor. This gives rise to a disadvantage that the circumferential speeds of teeth and bearings of gears as components of the speed change gear mechanism are necessarily increased and a noise level is increased.
Also, when the rotational speed of the speed change gear mechanism is equal to or greater than that of the main motor, the bearings for supporting the gears as components of the speed change gear mechanism are required to have a large load capacity for ensuring an improved useful life. This requirement however raises a problem that a seizing trouble is more likely to occur due to an increased value of dxc2x7n (d=bearing inner diameter, n=number of rotations).
The above-mentioned problems become more serious, particularly, in an extruder such as a biaxial continuous kneader, for which a scale-up has been keenly demanded in recent days, because a main motor must have larger power and rotate at a higher speed to satisfy such a demand.
In view of the state of the art set forth above, it is an object of the present invention to provide an extruder driving apparatus in which a speed change gear mechanism is disposed in a position allowing the speed change gear mechanism to rotate at a much lower rotational speed, whereby a noise level is reduced and a seizing trouble is more surely avoided.
To achieve the above object, the present invention is achieved with the following technical features.
An apparatus for driving an extruder, according to the present invention, comprises a main motor; a planetary gear mechanism driven by the main motor and outputting a driving force after reducing a rotational speed of the main motor; a speed change gear mechanism driven by an output of the planetary gear mechanism and outputting a driving force after adjusting an output rotational speed of the planetary gear mechanism; a plurality of rotor drive shafts arranged parallel to each other, each rotor drive shaft being provided at an end thereof on the extruder side with a coupling unit for connecting to a rotor; an output distributing gear mechanism driven by an output of the speed change gear mechanism and outputting a driving force to be distributed to the plurality of rotor drive shafts arranged parallel to each other; and a thrust bearing for supporting an end of each rotor drive shaft on the side opposite to the extruder.
In other words, the present invention provides an extruder driving apparatus mainly comprising a main motor, a planetary gear mechanism, an output distributing gear mechanism, coupling units for connection to rotors, and thrust bearings for bearing thrust forces imposed on rotor drive shafts, wherein a speed change gear mechanism for adjusting a rotational speed of each rotor drive shaft through replacement of one pair of gears by another pair having a different gear ratio is provided between the planetary gear mechanism and the output distributing gear mechanism.
With such an construction, since the speed change gear mechanism is disposed on the output side of the planetary gear mechanism, the rotational speed of each gear as a component of the speed change gear mechanism can be reduced down to a much lower value than that of the main motor (usually about ⅕ to {fraction (1/10)} of the motor rpm).
Accordingly, the circumferential speeds of teeth and a bearing of each gear as a component of the speed change gear mechanism are also reduced and noise from the driving apparatus can be lessened to a level as low as possible. Further, since a value of dxc2x7n of the bearing supporting each gear is reduced, a risk of seizing of the bearing can be avoided to the utmost.
A planetary gear mechanism has a structure that a plurality of planetary gears are meshed with a sun gear. Therefore, the vector sum of gear meshing forces acting on the sun gear becomes substantially zero, and the sun gear is subjected to only torque and substantially no radial forces. Also, since the torque is evenly distributed to the plurality of planetary gears, the sun gear is not required to be supported by a bearing. Because of those structural features, when a main motor is directly coupled to a planetary gear mechanism as with the present invention, problems of high noise and seizing of a bearing do not occur with the planetary gear mechanism.
In trying to separately provide a rotational-speed adjusting mechanism in a gearing wherein a planetary gear mechanism serving as a main speed reducer and an output distributing gear mechanism serving as a load distributor are combined with each other, it is general knowledge to those skilled in the art that the speed change gear mechanism is disposed on the input side of the planetary gear mechanism like the related art, for the simple reason that such an arrangement reduces torque acting on gears of the added mechanism. By contrast, in the present invention, the novel advantages described above can be obtained by providing the speed change gear mechanism between the planetary gear mechanism and the output distributing gear mechanism contrary to the general knowledge.
More particularly, in the present invention, the speed change gear mechanism may comprise a driver gear directly coupled to an output shaft of the planetary gear mechanism, and a driven gear held in mesh with the driver gear and directly coupled to an end of one of the rotor drive shafts which penetrates through the thrust bearing and is further extended to the opposite side. In this type of the speed change gear mechanism, preferably, the driven gear is formed with helical gear acting to push the one rotor drive shaft back toward the rotor side.
The reason is as follows. By forming helical gear on the driven gear so as to push the rotor drive shaft back toward the rotor side, the load of a thrust bearing for supporting a thrust force imposed on the rotor drive shaft is reduced and a smaller thrust bearing can be employed. Consequently, the size and cost of the driving apparatus can reduced down to the smallest and lowest possible level.
In a mechanism wherein the planetary gear mechanism is directly connected to the output distributing gear mechanism like the related art, its specific structure impedes an attempt of mitigating a thrust force imposed on the rotor drive shaft, which is directly coupled to an output shaft of the planetary gear mechanism, by using the same means as used in the present invention. Usually, spur of herringbone (double helical) gears are employed in a planetary gear mechanism, and therefore a thrust force cannot be intentionally produced on an output shaft of the planetary gear mechanism. Further, when helical gears are employed in a planetary gear mechanism, the sum of thrust forces acting on planetary gears is zero and hence a thrust force imposed on an output shaft of the planetary gear mechanism is also zero.
From the structural point of view, it is also difficult to mitigate a thrust force imposed on a rotor drive shaft directly coupled to an output shaft of the preceding stage by using a thrust force generating mechanism that is added in the output distributing gear mechanism. When attempting to mitigate the thrust force imposed on the rotor drive shaft, it would be unavoidable that large thrust forces are produced in directions to act on individual distributing shafts of the output distributing gear mechanism. Such an attempt is therefore not preferable because of the necessity of employing bearings having a large load capacity or bearings dedicated for thrust forces in order to support the distributing shafts.
Further, when attempting to mitigate a thrust force imposed on another rotor drive shaft different from one, which is directly coupled to an output shaft of the preceding stage, by using a thrust force generating mechanism added in the output distributing gear mechanism, such an attempt produces a thrust force imposed on the rotor drive shaft, which is directly coupled to the output shaft of the preceding stage, in a direction to increase the thrust force. Accordingly, when the thrust force imposed on another rotor drive shaft different from one, which is directly coupled to the output shaft of the preceding stage, is mitigated by using the thrust force generating mechanism added in the output distributing gear mechanism, it would be essential to employ some means for mitigating the thrust force imposed on the rotor drive shaft which is directly coupled to the output shaft of the preceding stage. The arrangement of the related art for mitigating only the thrust force imposed on another rotor drive shaft different from one, which is directly coupled to the output shaft of the preceding stage, is not preferable.
Thus, only direct coupling between the speed change gear mechanism and the output distributing gear mechanism as employed in the present invention makes it possible to mitigate the thrust force imposed on the rotor drive shaft which is directly coupled to the output shaft of the preceding stage.
Further, the present invention preferably employs a planetary gear mechanism including a rotatable hollow gear that has internal gear provided on an inner circumference thereof to be meshed with all planetary gears and a second torque input portion provided on an outer circumference thereof. Also, preferably, a speed-variable auxiliary driving mechanism for applying a driving force separately from the main motor is connected to the second torque input portion of the hollow gear. With these features, each rotor drive shaft can be operated at a speed variable steplessly within the speed change range provided by the auxiliary driving mechanism.
In this connection, by arranging an axis of a pinion shaft of the auxiliary driving mechanism to be coincident with an axis of the rotor drive shaft directly coupled to the output shaft of the speed change gear mechanism, it becomes easier to bore holes through bearings for supporting the pinion shaft and the driven gear of the speed change gear mechanism. Further, by arranging an auxiliary motor for driving the auxiliary driving mechanism adjacent to the main motor on the same side with respect to the planetary gear mechanism, the driving apparatus can be made more compact in an overall width.